A conventional method of testing for a leak with this type of double blow molded bottles involved testing the entire bottle for any leak, as by means of pressure measurement inside the bottle.
Because the aforementioned conventional leak testing method involves testing the entire double blow molded bottle for any leak, it was impossible to test these bottles for a leak unless each of the outer and inner vessels has a leak at the same position of the bottle. The leak test could not be conducted if the inner vessel alone had a leak.